The invention relates to a drive device which is intended for displacing two linearly movable components of a plastics injection-molding machine at least partly at successive times, in particular for displacing the injection unit for bringing the injection nozzle into contact with a mold and for displacing the injection mechanism for injecting polymer into the mold.
Such a drive device is known from U.S. Pat. No. 4,540,359. Used there is an electric rotating motor, to move an injection unit including the injection nozzle up to an injection mold and away from the mold again, in order in this way to execute the so-called nozzle forward movement, and to move an injection mechanism including a plasticizing screw axially, for injecting polymer into the injection mold. The two movements take place completely separately at successive times. The electric motor is fastened laterally to the housing of the injection unit, its axis running parallel to the direction of the nozzle forward movement and the injection movement. The rotating electric motor can be used firstly for driving, by means of a belt gear mechanism, a shaft mounted rotatably in the housing of the injection unit, which passes through a gear wheel, which is either freely rotatable with respect to the shaft or can be coupled to the shaft by means of an electromagnetically operable clutch. The gear wheel meshes with a further gear wheel, which is fastened in a rotationally secure manner on a threaded spindle, which together with a linearly guided spindle nut forms a threaded drive, by means of which the rotating movement of the electric motor and the following elements of the gear mechanism is transformed into a linear movement of the injection mechanism. The intermediate shaft can be coupled by means of a second electromagnetically operable clutch to a threaded spindle which is in line with the intermediate shaft, is held in an axially fixed manner on the housing of the injection unit and meshes with a spindle nut arranged in a fixed manner on the machine frame.
To bring the injection unit up to the injection mold, the latter clutch is operated, while the first clutch is inoperative. Consequently, the threaded spindle arranged in line with the intermediate shaft is rotated and, as a result, the injection unit is brought up to the injection mold. When this has taken place, a blocking device is operated, which device prevents rotation of the second threaded spindle in relation to the housing of the injection unit. The second clutch is deactivated.
Then, the first clutch is operated and, as a result, a force chain from the electric motor to the first threaded spindle, and consequently to the injection mechanism, is closed. The latter moves axially forward, whereby previously plasticized polymer is injected into the injection mold.
A disadvantage of the known drive device is that the clutches, the input element and output element of which are rotatable in relation to each other, are subjected to relatively high wear. Altogether, the known drive device is quite complex, and consequently also very expensive.